Method and device for transmitting data according to a hybrid arq method

ABSTRACT

The aim of the invention is to achieve a greater flexibility when transmitting data according to a hybrid ARQ method, (preferably when used in a mobile radio system. To this end, a channel-coded bit stream is divided into at least one first bit stream (A) and one second bit stream (B, C), whereby these parallel bit streams (A-C) are each subjected to a separate bit rate matching, and the resulting bits of the individual bit streams (A-C) are subsequently combined with one another once again in order to transmit in a data packet or in a repeat data packet that is requested on the receiver side.

[0001] This invention relates to a method and a correspondingly designed device for transmitting data according to a hybrid ARQ method in a communication system, in particular a mobile radio system.

[0002] The use of so-called packet access methods or packet-oriented data connections is often recommended especially in connection with mobile radio systems, since the message types produced often have a very high burst factor with the result that only short periods of activity exist, interrupted by long rest phases. Packet-oriented data connections may in this case considerably increase efficiency compared to other data transmission methods in which a continuous data stream is present, since, in data transmission methods with a continuous data stream, once a resource has been allocated, such as—for example—a carrier frequency or a time slot, it remains allocated during the entire communication relationship, i.e. a resource remains occupied even if there are momentarily no data transmissions taking place, which means that this resource is not available for other network users. The result is that the narrow frequency range available for mobile radio systems is not used to best effect.

[0003] Future mobile radio systems, such as—for example—those that comply with the mobile radio standard UMTS (Universal Mobile Telecommunications System), will offer a multitude of different services whereby multimedia applications will become increasingly prevalent alongside pure voice transmission. The diversity of services associated with this, with different transmission rates, requires a highly flexible access protocol on the air interface of future mobile radio systems. Packet-oriented data transmission systems have proved to be highly suitable in this context.

[0004] In connection with UMTS mobile radio systems, a so-called ARQ (Automatic Repeat Request) method has been proposed in packet-oriented data connections. In this method the data packets transferred from a transmitter to a receiver are checked for quality at the receiving end following decoding. If a data packet is errored on receipt, the receiver requests retransmission of this data packet by the transmitter, i.e. a repeat data packet which is identical or partially identical to the one previously sent and which was errored on receipt, is sent from the transmitter to the receiver, (the terms full or partial repeat are used to indicate whether the quantity of data contained in the repeat data packet is less than or equal to that of the original data packet). With regard to the ARQ method proposed for the UMTS mobile radio standard, the intention is for both data and so-called header information to be transmitted in a data packet, whereby the header information also contains information for error checking, e.g. CRC (Cyclic Redundancy Check) bits, and can also be coded for error correction (known as FEC, Forward Error Correction).

[0005] In accordance with the current proposals for the UMTS specification, it is planned to introduce a so-called hybrid ARQ method which is also known as the Incremental Redundancy ARQ method. The main difference compared to the conventional ARQ method described above is that a coding process is carried out in the receiver using several data packets with the same information source but different channel coding. In other words, several data packets with the same information source are decoded and evaluated until an originally transmitted data packet is deemed to have been decoded as error-free in the receiver. In contrast to the previously described ARQ method, in the hybrid ARQ method the repeat data packets (which are also called “retransmission”) are not normally identical to the data packet originally transmitted.

[0006]FIG. 3 shows the signal processing for the hybrid ARQ method under discussion in accordance with the current status of UMTS standardization.

[0007] As shown in FIG. 3, the generation of the transmission signal is subdivided into the processing of the actual data and the processing of the header information. On the header side the header information created by a function block 3 is supplied to a function block 12, which ensures that all headers of all data packets that are to be transmitted in the same radio packet are linked together into a single header (header concatenation). A function block 13 inserts CRC bits for error detection into the resulting header information. The resulting bit stream is then subjected to channel coding by a function block 14 and rate matching by a function block 15. An interleaver, 16, causes the symbols and/or bits supplied to it to be arranged in a particular way and time-interleaved. The data blocks produced by the interleaver 16 are allocated by a function block 17 to the individual transmit or radio frames (known as radio frame segmentation).

[0008] A function block 4 is also provided on the data side for the insertion of CRC bits. A function block 5 is used for splitting the data supplied to a channel coder 6 such that a coding process limited to a specific number of bits can always be carried out by the channel coder 6.

[0009] Because of the channel coding carried out by the channel coder 6, the actual data to be transmitted has redundant information inserted in it with the result that several consecutively transmitted data packets have bits with the same information origin. In the hybrid ARQ method (as per so-called Types II and III), if a data packet is incorrectly received or decoded by the receiver, the transmitter does not send the same packet again to the receiver but instead transfers a data packet which has at least some bits with the same information source as the bits contained in the data packet originally transferred. The receiver, by evaluating together all data packets containing bits with the same information source, can retrieve the originally transmitted information with better quality.

[0010] In order to implement the hybrid ARQ method described above, it is necessary, if so requested by the receiver, for the data transmission signals with incremental redundancy which are received in the originally transmitted data packet and the corresponding repeat data packets to be generated from the same information source (so-called redundancy selection). For this purpose, after the channel coder 6 a corresponding function block 7 is provided, which is controlled by the function block 3 as a control entity and carries out a corresponding bit selection process after the channel coding. In this way the bits to be transmitted in the first packet and in repeat data packets are selected by the function block 7 according to the control exercised by the function block 3.

[0011] The data produced by function block 7 is supplied to a function block 8, which adjusts the bit rate of the data stream by masking or omitting individual bits (known as puncturing) or repeating individual bits. So-called DTX (Discontinuous Transmission) bits can be inserted into the data stream by a subsequent function block 9. Also provided on the data side are function blocks 10 and 11, which perform the same functions as do function blocks 16 and 17 on the header side.

[0012] Finally the bits produced on the data and header side are mapped or multiplexed by a function block 18 on whatever physical transfer or transmission channel is available at the time.

[0013] To ensure that the hybrid ARQ method or incremental redundancy ARQ method operates with maximum efficiency, the FEC coding of the various data repeat packets should where possible be selected such that these data packets typically have very little concurrence between them. This is particularly problematic in the case of UMTS because of the high flexibility of the channel coding and data matching carried out with regard to the individual transmission channels, in particular since the channel coding cannot be optimized solely in terms of its efficiency. Other factors are also involved in this, for example the memory requirement and the complexity of the algorithms executed, an essential role since this particularly affects the algorithms executed on the part of the mobile station.

[0014] In general, the problem with the hybrid ARQ method explained using FIG. 3 is that of how best to code an originally transmitted data packet, and possibly one or more subsequently transmitted repeat data packets, in order to achieve maximum benefit.

[0015] This invention is therefore based on the object of proposing a method and a correspondingly designed device for transmitting data according to a hybrid ARQ method, that enables the principle of a hybrid ARQ method to be implemented with increased flexibility and better use of the potential coding gain without significantly increasing the complexity and the memory requirement.

[0016] This object, according to the invention, is achieved by a method with the features of claim 1 and a device with the features of claim 23. The subordinate claims define in each case preferred and beneficial embodiments of this invention.

[0017] The basic idea behind this invention is to combine the function blocks 7 and 8 for redundancy selection and rate matching shown in FIG. 3, so that a more efficient coding process can take place. Thus the function blocks 7 and 8 of the hybrid ARQ structure shown in FIG. 3 are replaced in particular by a structure which carries out a bit separation process in order to generate several (differently coded) parallel bit streams with subsequent bit collection. The different bit streams are each subjected to rate matching independently of one another. In this way greater flexibility is achieved with the coding. For each data packet or repeat data packet to be transmitted, the different parallel bit streams can be combined with one another, preferably in proportion. This can be implemented particularly effectively in the case of bit repetition.

[0018] The advantage of the proposed method and/or the corresponding device according to the invention is greater flexibility and better use of the potential coding gain, whilst also enabling a less repetition-based rate-matching to be achieved without any significant increase in complexity and memory requirement (the latter would be required in particular for the interleaving).

[0019] Preferred embodiments of this invention are described in the subclaims, which relate in particular to the method of bit separation and bit collection executed according to the invention and the choice of rate matching for the various different bit streams which result from the bit separation process.

[0020] This invention is explained in greater detail below with reference to the attached drawing on the basis of preferred embodiments of packet-oriented data transmission in a mobile radio system, whereby the invention is of course not limited to mobile radio systems, but can be used generally in any type of communication system in which a hybrid ARQ method is provided for data transmission.

[0021]FIG. 1 is a diagram for clarifying signal processing, in particular according to a packet-oriented hybrid ARQ method of this invention,

[0022]FIG. 2 is a diagram for clarifying the communication in a mobile radio system, and

[0023]FIG. 3 is a diagram for clarifying the signal processing according to a conventional packet-oriented hybrid ARQ method.

[0024] As already explained, the following is based on the idea that packet-oriented data transmission in a mobile radio system, as shown schematically in FIG. 2 by way of example, is to be implemented with the help of this invention. Thus FIG. 2 shows by way of example the communication between a base station 1 and a mobile station 2 of a mobile radio system, for example a UMTS mobile ratio system. The transmission of information from the base station 1 to the mobile station 2 takes place via the so-called downlink channel DL, whilst the transmission of information from the mobile station 2 to the base station 1 takes place via the so-called uplink channel UL. This invention is explained below using as an example a packet-oriented data transmission from the base station 1 to the mobile station 2, i.e. a packet-oriented data transmission via the downlink channel, in which the invention can however also be used similarly on data transmission via the uplink channel. This invention is further explained below analogously to FIG. 3 on the basis of the signal processing measures to be executed in the transmitter concerned, whereby it is important to note that a corresponding signal processing operation in the reverse sequence is required in the relevant receiver for evaluation of the data processed in this way at the transmitter end, which means that this invention affects not only the transmitter end but also the receiver end.

[0025]FIG. 1 shows the signal processing of the data and header information to be transferred in data packets following a hybrid ARQ method according to the invention. This invention mainly affects the processing of the data part, so that the function blocks 12-17 shown in FIG. 1 that affect the header part correspond to the function blocks 12-17 shown in FIG. 3. Likewise the function blocks 3-6, 9-11, and 18 shown in FIG. 1 correspond to the function blocks with the same numbers in FIG. 3, which means that the above explanations concerning FIG. 3 can also be used with reference to the purpose and function of these function blocks.

[0026] As can be seen from FIG. 1, the function blocks 7 and 8 as shown in FIG. 3 have been replaced by a new function section 19. This function section 19 includes a function block 20, which—dependent upon control exercised by the function block 3—separates the coded bits produced by the upstream channel coder 6 into at least two parallel bit streams, which are each subjected to rate matching separately, i.e. independently of one another. In this regard FIG. 1 shows three bit streams, each of which has one function block 21-23 provided for rate matching, i.e. for puncturing or repetition of individual bits. This results in several differently coded parallel bit streams, which are supplied to a further function block 24. This further function block 24 has the task of collecting the individual bits from the parallel bit streams in the same sequence that was used by function block 20 for the bit separation process, i.e. for the separation into the individual parallel bit streams. This is to ensure that the sequence of bits remaining after rate matching remains unchanged overall.

[0027] If one of these parallel bit streams is selected exclusively for each data packet, the signal processing method as per FIG. 1 can be transferred to the signal processing method as per FIG. 3. However, it can be seen that the signal processing method shown in FIG. 1 enables greater flexibility to be achieved in coding. In particular, it is possible for the different parallel bit streams to be combined with one another proportionally for each data packet, this being particularly useful in the case of bit repetition. Thus, for example, instead of applying a purely repetition-based coding to a single bit stream, as would be the case in the repetition-based coding shown in FIG. 3, in the signal processing method shown in FIG. 1 the bit stream A can be transferred unchanged, i.e. without carrying out a rate matching process, whilst at the same time the bit stream B shown in FIG. 1 can be used with appropriate rate matching to pad the remaining transmit signals. In particular, the separation of the bits from the channel-coded bit stream into the individual bit streams A-C may be selected such that only bits from the bit streams 1 to N are used for a data packet or repeat data packet. This is not possible according to the prior art shown in FIG. 3 and can only be implemented by the principle proposed in accordance with the invention, as shown in FIG. 1 by way of example. This variant has the advantage that only memory for N bit blocks needs to be reserved in the receiver for receiving the repeat data packet no. N, since it is already known that the received data only comes from these N bit blocks. More generally, a scheme can also be devised whereby the number of bit blocks used for the repeat data packets 1 to N increases monotonically or even strictly monotonically with N.

[0028] Preferred embodiments for the bit separation and bit collection processes carried out by function blocks 20 and 24 respectively and for the rate matching processes carried out by function blocks 21 to 23 are to be explained below.

[0029] In view of the choice of parallel rate matching samples which are implemented by function blocks 21 and 22 and—if necessary—23, provision can be made for these to be selected such that a function is executed by the entire function section 19, which is equivalent to the function exercised by function blocks 7 and 8 shown in FIG. 3 according to the current state of the specification.

[0030] During repetition the data packets can likewise be padded with data from more than two parallel bit streams A-C, such that the bits from one bit stream or branch are transferred in their entirety, i.e. unchanged, while the bits from the other bit streams or branches are used to pad the remaining data. According to a further embodiment the rate matching sample may also be selected such that the data packets used in repetition are padded with data from exactly two parallel bit streams, whereby one bit stream is transferred in its entirety, i.e. unchanged, while the other bit stream is used to pad the remaining data.

[0031] The functioning of function blocks 20 and 24 can be selected such that an original data packet to be transmitted always contains data from bit stream A, or—if the data from bit stream A is already being transferred in its entirety—data from bit streams A and B. For the first repeat data packet, then, data from bit stream B is used in preference, or—if the data from bit stream B is already being transferred in its entirety—data from bit streams B and A. For the second repeat data packet it is particularly beneficial to use data from bit stream C, or—if the data from bit stream C is already being transferred in its entirety—data from bit streams C and B.

[0032] In general the aim is to use the memory in the mobile station 2 as efficiently as possible by combinations, and thus to avoid spreading data in the data packets too greatly with regard to its origin. In addition, it should also be possible to make use of a maximum gain in terms of coding.

[0033] An optimum selection in terms of memory requirement for mobile station 2 is explained below, whereby the embodiment explained subsequently represents a compromise between the memory requirement and the efficiency to be expected. In accordance with this embodiment, bits to be repeated are selected only from such branches or bit streams whose data is already being transferred according to the prior art as per FIG. 3, whereby an increased memory requirement, particularly in the receiver, is avoided. According to this embodiment the original data packet contains only data from bit stream A. The first repeat data packet contains data from bit stream B, or—if the data from bit stream B is already being transferred in its entirety—data from bit streams B and A. To this extent, this embodiment is the same as the one described above. However, unlike in the embodiment described above, the second repeat data packet contains data from bit stream C, or—if the data from bit stream C is already being transferred in its entirety—data from bit stream C and from bit stream B and/or bit stream A.

[0034] It is generally advisable, after exactly one repetition has been requested, to transfer bit streams A and B in roughly equal bit quantities. After exactly two repetitions have been requested, bit streams A, B and C should be transferred in roughly equal bit quantities.

[0035] Of course, all the embodiments described in this patent application may in general be applied to more than two repetitions.

[0036] According to a further variant of this invention, a large proportion of the data can be punctured following the coding process by the channel coder 6 of those branches and/or bit streams A-C, which are not primarily for transmission, since only a small proportion of the bits to be transferred (typically 10%, for example) are selected anyway from these bit streams by the subsequent rate matching. Therefore it does not matter if 90% of the bits from these branches and/or bit streams are deleted immediately. This measure means that a correspondingly smaller memory space is required in the interim function blocks, so that this variant primarily aims to reduce the memory requirement further.

[0037] The variant described below is equivalent to the last variant mentioned above. Instead of selecting a specific bit stream (e.g. bit stream B) with subsequent puncturing of 90%, two bit streams may also be introduced instead of this bit stream (e.g. bit stream B′and bit stream B″), whereby one bit stream (B′) contains 10% of the bits of the original bit stream (B). 

1. Method for data transmission according to a hybrid ARQ method, wherein data is transferred from the transmitter (1) to a receiver (2) in the form of data packets, wherein at least one repeat data packet is transferred to the receiver (2) from the transmitter (1) after a data packet has been transmitted, if a corresponding request is issued by the receiver (2), wherein the repeat data packet and the data packet originally transmitted have bits with the same information source, wherein, in order to select the bits to be transferred in the repeat data packet, a bit selection process is carried out with regard to a channel-coded bit stream, wherein the bits to be transferred in the data packet or the repeat data packet are subjected to a bit rate matching process, wherein the bit selection and the bit rate matching process are carried out together, so that the bits from the channel-coded bit stream are separated into at least a first bit stream (A) and a second bit stream (B, C), and the individual bit streams (A-C) are each subjected to a separate bit rate matching process, wherein the separate bit rate matching processes applied to the first bit stream (A) and the second bit stream (B, C) are selected such that: the bits of the first bit stream (A) are used unchanged for a data packet and bits of the second bit stream (B, C) are used for padding the data packet, and the bits of the second bit stream (B, C) are used unchanged for a repeat data packet and bits of the first bit stream (A) are used for padding the repeat data packet, and wherein bits that have been individually channel-coded by the corresponding separate bit rate matching process are only repeated if all bits from the channel-coded bit stream are selected for transmission during bit rate matching.
 2. Method according to claim 1, characterized in that the bit rate matching process applied to the individual bit streams (A-C) is selected such that for the data packet or repeat data packet the bits of the first bit stream (A) are used unchanged and the bits of the first and second bit stream (B, C) are used for padding the data packet or repeat data packet.
 3. Method according to one of the above claims, characterized in that the separation of the bits of the channel-coded bit stream is selected such that the originally transmitted data packet contains bits from the first bit stream (A) and bits from the second bit stream (B).
 4. Method according to one of the above claims, characterized in that the separation of the bits of the channel-coded bit stream is selected such that the repeat data packet contains bits from the second bit stream (B).
 5. Method according to one of the above claims, characterized in that the separation of the bits of the channel-coded bit stream is selected such that the repeat data packet contains bits from the second bit stream (B) and bits from the first bit stream (A).
 6. Method according to one of the above claims, characterized in that the bits from the channel-coded bit stream are separated at least into a first bit stream (A), a second bit stream (B), and a third bit stream (C), and the individual bit streams (A-C) are each subjected to a separate bit rate matching process, and the separation of the bits of the channel-coded bit stream is selected such that a further repeat data packet, transmitted after the originally transmitted data packet and the repeat data packet, which has bits with the same information source as the originally transmitted data packet and the repeat data packet, contains bits from the third bit stream (C).
 7. Method according to one of the above claims, characterized in that the bits from the channel-coded bit stream are separated at least into a first bit stream (A), a second bit stream (B), and a third bit stream (C), and the individual bit streams (A-C) are each subjected to a separate bit rate matching process, and the separation of the bits of the channel-coded bit stream is selected such that a further repeat data packet, transmitted after the originally transmitted data packet and the repeat data packet, which has bits with the same information source as the originally transmitted data packet and the repeat data packet, contains bits from the third bit stream (C) and bits from the second bit stream (B).
 8. Method according to claim 1, characterized in that the separation of the bits of the channel-coded bit stream is selected such that the originally transmitted data packet contains only bits from the first bit stream (A).
 9. Method according to claim 8, characterized in that the bits of the channel-coded bit stream are separated at least into a first bit stream (A), a second bit stream (B), and a third bit stream (C), and the individual bit streams are each subjected to a separate bit rate matching process, and the separation of the bits from the channel-coded bit stream is selected such that a further repeat data packet, transmitted after the originally transmitted data packet and the repeat data packet, which has bits with the same information source as the originally transmitted data packet and the repeat data packet, contains bits from the third bit stream (C).
 10. Method according to claim 8, characterized in that the bits of the channel-coded bit stream are separated at least into a first bit stream (A), a second bit stream (B), and a third bit stream (C), and the individual bit streams (A-C) are each subjected to a separate bit rate matching process, and a further repeat data packet, transmitted after the originally transmitted data packet and the repeat data packet, which has bits with the same information source as the originally transmitted data packet and the repeat data packet, contains bits from the third bit stream (C) and bits from the first bit stream (A) and/or the second bit stream (B).
 11. Method according to one of the above claims, characterized in that the separation of the bits of the channel-coded bit stream into the individual bit streams (A-C), the bit rate matching applied to the individual bit streams (A-C), and the subsequent combination of the individual bit streams (A-C), are selected such that after the transmission of the data packet and the repeat data packet, the quantities of bits transferred from the first bit stream (A) and the second bit stream (B) are at least roughly the same.
 12. Method according to one of the above claims, characterized in that the bits of the channel-coded bit stream are separated at least into a first bit stream (A), a second bit stream (B), and a third bit stream (C), and the individual bit streams (A-C) are each subjected to a separate bit rate matching process, and the separation of the bits of the channel-coded bit stream into the individual bit streams (A-C), and the bit rate matching applied to the individual bit rates (A-C) are selected such that after the transmission of the originally transmitted data packet, the repeat data packet and a further repeat data packet, which has bits with the same information source as the originally transmitted data packet and the repeat data packet, the quantities of bits transferred from the first bit stream (A), the second bit stream (B) and the third bit stream (C) are at least roughly the same.
 13. Method according to one of the above claims, characterized in that bits of those bit streams (A-C) whose bits are momentarily in relationship to the other bit stream or bit streams but are not primarily intended for transmission in the data packet or repeat data packet being transmitted at that time, are partially removed from this bit stream (A-C) before application of the corresponding bit rate matching process to this bit stream (A-C).
 14. Method according to claim 13, characterized in that about 90% of the bits of those bit streams (A-C) which are momentarily in relationship to the other bit stream or bit streams but are not primarily intended for transmission in a data packet or repeat data packet to be transmitted at that time, are deleted from the bit stream (A-C) before application of the corresponding bit rate matching process to this bit stream (A-C).
 15. Method according to one of the above claims, characterized in that the method is executed in a mobile radio system.
 16. Method according to one of the above claims, characterized in that the separation of the bits of the channel-coded bit stream into the individual bit streams (A-C) is selected such that the number of bit blocks used for repeat data packets no. 1 to N increases with N.
 17. Method according to claim 16, characterized in that the separation of the bits of the channel-coded bit stream into the individual bit streams (A-C) is selected such that only bits from bit streams no. 1 to N are to be used for a repeat data packet no. N.
 18. Device for data transmission according to a hybrid ARQ method, whereby data is transferred from the device (1) to a receiver (2) in the form of data packets, whereby the device (1) is designed such that data is transmitted from a transmitter (1) to a receiver (2) in the form of data packets, such that at least one repeat data packet is transferred to the receiver (2) by the transmitter (1) after transmission of a data packet, if a corresponding request is issued by the receiver (2), such that the repeat data packet and the originally transmitted data packet have bits with the same information source, such that bit selection with regard to a channel-coded bit stream is carried out in order to select the bits to be transferred in the repeat data packet, such that the bits to be transferred in the data packet or repeat data packet are subjected to bit rate matching, such that the bit selection and bit rate matching processes are carried out together, such that the bits from the channel-coded bit stream are separated into at least a first bit stream (A) and a second bit stream (B, C), and the individual bit streams (A-C) are each subjected to a separate bit rate matching process, such that the separate bit rate matching processes applied to the first bit stream (A) and the second bit stream (B, C) are selected such that: the bits of the first bit stream (A) are used unchanged for a data packet and the bits of the second bit stream (B, C) are used for padding the data packet, and the bits of the second bit stream (B, C) are used unchanged for a repeat data packet and bits of the first bit stream (A) are used for padding the repeat data packet, and such that bits that have been individually channel-coded by the corresponding separate bit rate matching process are only repeated if all bits of the channel-coded bit stream are selected for transmission during bit rate matching.
 19. Device according to claim 18, characterized in that the device (1) is designed for executing the method according to one of the claims 1-17.
 20. Receiver (2) for receiving data transferred in the form of data packets according to a hybrid ARQ method, characterized in that the receiver (2) is designed for receiving, decoding and evaluating a data packet or repeat data packet transferred according to the method described in one of the claims 1-17, in order to determine the information content of the data transferred in the data packet. 